Even in the present day when a large number of infectious diseases are conquered, malignant tumors are one of the most serious diseases with which human beings are now confronted. Although treatment methods for malignant tumors have been proposed one after another and the therapeutic ratio has been increased, early stage diagnosis of malignant tumors is the most important factor in treating malignant tumors. Accordingly, various types of tumor markers have been proposed for diagnosing malignant tumors at an early stage and various diagnostic agents have already been on the market, but they have problems still remained unsolved in terms of their efficacy. Although a higher value of a tumor marker indicates higher possibility of a malignant tumor, no information can be obtained on the site where the malignant tumor is present.
It has been found recently that hematoporphyrin and derivatives thereof (so called porphyrins) accumulate in malignant tumors specifically, and methods for diagnosing malignant tumors have been developed using the property of these compounds to generate fluorescence by light irradiation. It is known that photophrin® as a typical compound of porphyrins generates an active oxygen by light irradiation to destroy malignant tumors, so that it has been approved as a therapeutic drug for malignant tumors, and a therapeutic method using this compound has been drawing attention as a photokinetically therapy (Life Science of Porphyrin and Heme, edited by Porphyrin Research Society, Tokyo Kagaku Dojin (1995)).
It was found in 1994 that protoporphyrin IX which is induced by administration of 5-aminolevulinic acid accumulates in tumors and shows similar effects to porphyrins, and this compound has been drawing attention due to its low toxicity and phototoxicity and quick metabolism in the body in comparison with those of the above-described porphyrins. It is disclosed that by applying this effect, 5-aminolevulinic acid is used as a contrast medium for MRI (magnetic resonance imaging) by replacing a portion of its hydrogen atoms with deuterium (D) (WO 97/03042).
However, the sensitivity of MRI using this contrast medium is not always satisfactory.
In consequence, an object of the present invention is to provide a diagnostic agent which accumulates properly in malignant tumors and can specify the site of tumor with high sensitivity using nuclear magnetic resonance and an agent for photokinetically treating malignant tumors.